Sound-detecting device



April 15, 1924. 1,490,742

A, W. HULL 'SOUND DETECTING DEVI-CE Filed June 6, 1919 His Abbot-nes.

Patented Apr. 15, 1924.

UNITED STATES 1,490,742 PATENT OFFICE.l

' ALBERT W. HULL, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

SOUND-DETECTING DEVICE.

Application led J'une 6,

To all 'whom z't may concern Be it known that I, ALBERT W. HULL, a citizen of the United States, residin at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Sound-Detecting Devices, of which the following is a specification.

My invention relates to devices for detecting sounds or similar vibrations trans mitted through a fiuid medium such as water or the like, in which the sounds are rendered perceptible through the instrumentality of a telephone receiver connected to a microphone, or similar electric device, located in a closed chamber having a yielding or resilient wall.

In the practical use of sound detectinor devices of the general character indicated the vibrations impressed thereon by reason of the sound waves to which it may be exposed, subject the air in the enclosed chamber in the device to corresponding waves of eXpansion and contraction. Microphones of the inertia type comprising a ti ht casing which -contains carbon granules etween carbon terminals are suitable for sound detecting devices of this character.V I have found that the varying air pressure roduced within the enclosed chamber containing the microphone may produce a marked effect by varyingk the pressure exerted upon the carbon granules through the medium of the carbon terminals, and thereby varying the resistance of the microphone before the air has had a chance to leak back or forth through the joints in the microphone casing. These pressure eects are peculiarly noticeable when the sound detecting device is submerged in water, the surface of which is more orless agitated by waves, as the changes in hydrostatic pressure produced upon the sound detecting device by the rise and fall of the waves becomes so distinctly noticeable in the microphone, that a listener hears sound due to the waves. In order to eliminate these wave sounds I provide the microphone. of the inertia type described with Ventilating openings for immediately equalizing the air pressure within the mass of carbon granules in the interior .of the microphone and the pressure of the air outside of the microphone. As a result, the

pressure of the air in the closed chamber may be changed by changes in the hydro- 1919. Serial No. 302,232.

static head on the flexible wall of the chamber Without producing any change in the pressure exerted upon the carbon granules of the microphone, because pressure changes are instantly equalized by reason of the ventilating openings, and therefore no pressure change is exerted on the vcarbon granules.

In carrying out my invention in practice, I utilize a microphone of the inertia type so arranged as to receive the vibrations from the Huid medium through the vibrations of an interposed body of a material suh as soft rubber having non-resonant, aperiodic characteristics.`

The scope of my invention will be particularly pointed out in the appended claims, while the invention itself will be better understood by reference to the following description and the accompanying drawings, in which the device embodying my invention is illustrated by an enlarged longitudinal sectional view.

The sound receiving device made in accordance with my invention, Ithough not necessarily limited to use under water is nevertheless primarily adapted for that purpose, and to this end it is constructed so that its interior working parts shall be maintained free from water or moisture. In the particular form indicated in the drawings a cup-shaped member 1, best constructedD of pure soft Para rubber, contains the microphone element, which is carried on a perforated metallic disk 2 embedded in the rubber and having a perforated shank 3 projectin centrally into the interior or inner side o the cup. The rubber, which is molded about this perforated disk at the time the cup 1 is being formed, penetrates the openings or perforations in the disk 2 from side to side land thus-,firmly secures or scws it in place. The microphone element is supported on the 'shank 3, which is centrally drilled and tapped to hold it. This microphone element, shown partly in section on the drawing, and in the main of usual construction, comprises a brass casing or cup 4 containing carbon granules 5 inI contact with one carbon plate or terminal 6 resting on the bottom of the cup and also with a second carbon plate or terminal 7, electroplated on one side, and soldered on that side to a disk 8 of the cup is closed by a perforated mica diaphragm 11 clamped between the disk 8 and a. disk 12 of brass or other suitable material threaded on the projection 9 of the brass disk 8,-and screwed down against the mica` diaphragm` The brass casing or cup 4 has a threaded supporting stud 13 integral with or riveted to it to screw into the shank 3 and support the microphone in place.

To assist in making electrical connections to the microphone in such a manner that movement of the microphone does not cause variations lof pressure on the carbon granules, I"`provide a bail 14, of brass or other conducting material, fastened to a metal ring spun about the flaring lip of the cup 4 and in electrical contact through the cup with the carbon terminal 6. A flexible terminal wire 15 leading to the microphone is mechanically and electrically connected to the bail 14 While the other iiexible terminal wire 16 is mechanically connected to but insulated from the bail by an insulated terminal 17, which is connected through a very flexible wire 18 to the threaded projection 9 and thence to the carbon plate or terminal 7.

To enclose the microphone in a watertight chamber, I close the open end of the rubber cup 1 with some suitable water-tight closure. I prefer a thimble or short tube 19 having external circumferential grooves and fitted tightly into the rubber cup 1. This thimble is counterbored at the outer end to receive various members which cooperate to produce a water-tight closure, while the open inner end of the thimble leaves the bottom of cup free to act as a diaphragm. A brass disk 2O fitting snugly in the counterbore of the thimble 19 has on its edge a groove for holding a drying agent, preferably metallic calcium in the form of a number of turns of wire 21. The slow diffusion of the air contained in the interior of the thimble and cup 1 through openings 22 into the groove 21 and over the calcium wire keeps the air perfectly dry. v

Electrical connections with the microphone are made through the terminal wires 14 and 15 by leading-in wires 23 and 24 heavily coated with rubber 25 and 26 and Afitting tightly into holes in the brass disk i 2O and also into holes in a solid block 27 of soft rubber which presses against the grooved brass disk 20. To compress the rubber 27 firmly about the wires and against the disk I provide a follower disk 28, preferably of brass, and having holes for the wires. The follower disk is driven a','gainst the rubber block 27, expanding itoutwardly against the thimble 19 and inwardly against the leading-in wires to form an absolutely Water-tight joint, by means of a follower ring 29 screw threaded into the outer end of the thimble 19. A lock washer 30 of hosphor bronze or similar spring metal etwcen the follower disk and the ring keeps the parts under constant compression in case they should have a tendency to give through the action of time or other influences.

In many cases it is advisable to clamp the rubber cu 1 to the thimble 19 clamp 31, lockedp by a screw fastener 32 in place ground the cup so as strongly to compress it against the thimble.

To protect the leading-in conductors 23 and 24 and the other portions of the device projecting from the cup 1 a soft rubber cover 33, through which the leading-in conductors pass, is applied over the projecting portion of the thimble 19. A reentrant portion 34 of this cover fits into the interior of the follower ring 29.

lVhen the device above described is iminersed in a sound conducting liquid medium the sound waves act upon the bottm of the cup 1, which forms a rubber diaphragm for supporting the microphone, and cause vibrations to be transmitted to the carbon ganules and carbon terminals by reason of the inertia of the parts of the microphone. As already explained, the variations in resistance of the microphone circuit due to these sound vibrations may be disturbed, in case the device is used in the open sea, by variations in the hydrostatic head of water above the device due to the rise and fall of the waves. The pressures due to water waves are applied and released very slowly, as compared with the rapid varying pressures produced by a sound wave, and cause a slow oscillation of the diaphragm, so that the microphone is moved bodily back and forth. Any effect upon the microphone of this slow movement of the rubber diaphragm is prevented by eliminating any factor which would make the microphone button sensitive to slowly applied pressure. To this end the terminal wires 14 and 15 leading to the microphone from the leads 23 and 24 are very flexible and are fastened mechanically to the bail 12 so that as the microphone is moved back and forth by the slow oscillation of the diaphragm these wires cause no variation in the pressure on the carbon granules of the microphone.

Changes in air pressure in the closed chamber produced by the oscillations of the rubber bottom of the cup 1 also vary the pressure on the carbon granules if the casing 5 of the microphone is tight. To prevent these pressure variations the brass casing 4 may be Ventilated by perforations 35 which equalize the pressure in the closed chamber and in the casing'4.

I do not lay claim to the bail 12 for the microphone as heretofore described nor to the use of rubber as a supporting diaphragm for the microphone, as-these features are de- .scribed andvcl'aimed in com anion applica- `.27 9 and. Chester W.

tions of Iryging Lan uir erial No. 302,-

ice Serial No. 302,247.

Sound detecting devices such as herein described ma` be used singly if desired, but are especia y useful in palrs or in triplets, for determining the direction from which a sound comes b means of the binaural sense possessed by't e human ears. When sound 1s transmitted to the human ears from a point which is not equally distant from the two ears of the observer, the sound arrives at one ear later than at the other because of the different distances which the sound has to travel to reach the two ears. The same sound impulses are therefore not received simultaneously at the two ears of the observer and in some way due to this effectthe brain receives the impression that the sound is either at the one side or the other of the observer. This eect is less pronounced the purer the. quality of the sound received. In the case, for example, of a pure tone such as that of a tuning fork or a telephone receiver actuated by sine wave alternating current the binaural sense can only withgreat diiiiculty determine the direction of the sound. Where, however, the sound includes sharp peaks or other salient and recognizable variations'or characteristics the binaural eect is much more acute. The use of a soft rubber diaphragm to support the microphone as heretofore described is of especial value where devices of this general character are to be used binaurally, as it avoids an resonance eEects such as might occur if 'aphragms of metal, wood or the like were employed, which resonance effects would, by magnifying sound vibrations forming no essential portion of the sounds to be listened to, have a tendency to produce a false uality in the sound perceived through t e microphone. As the binaural sense seems to depend upon some kind of comparison of some salient characteristics of the sound to be listened to, this sense is interfered with seriously where a false reproduction of the received soundsl is produced by resonant effects produced in the receiving apparatus itself.

While I have showna microphone of the carbon granule type it is evident that microphones of other varieties may be employed as well as devices of any other character such as magneto-phones or the like which will have the effect-of producing variations in an electric current, in response to the vibrations of the rubber vibratory diaphragm herein shown. While other material having the desired characteristics of soft rubber may be employed in place thereof, soft rubber gives the best results for the purposes in hand of any material with which I am acquainted.

It is to be observed that in the device which I have disclosed the rubber diaphragm supporting or carrying the microphone is in an unstrained and unstretched condition and I consider this a'valuable quali The fact that rubber is of approximate y the same densit as water, in which it is immersed, contri utes to the non-resonant quality of the diaphragm under the conditions of use.

What I claim as new and desire to secure' by Letters Patent of the United States, is,-

1. An under-water sound detecting device having in combination a water-tight body adapted for submerged use, "a' chamber in said body and a microphone in said chamber, said chamber having a flexible wall vibratory in response to sound waves and movable back and forth with variations of pressure which are caused by water waves above the device, said microphone cooperating with said flexible wall and comprising a casing containing granular materlal, and a cover for said casing, and vents in said casing, said vents permitting air to iow into and out of said casing as thepressure of the air in said chamber varies in response to the back and forth movement of the iexible wall caused by the water waves.

2. An under-water sound detecting device Y having in combination a water-tight body -adapted for submerged use, a chamber 1n said body provided with a iiexible wall vibratory in response to sound waves and movable back and forth with variations of pressure which are caused b waves above the device, and an inertia microphone mounted in said chamber on said flexible wall and comprising a casing containing granular material, and a cover for said casing, and vents in said casing, said vents permittin air to flow into and out of said casing as t e pressure in said chamber varies in response to the back and forth movement of the flexible wall which is caused by the water waves.

3. An under-water sound detecting device having in combination a water-tight body adapted for submerged use, a chamber in said body, said chamber having a rubber wall vibratory in response tolsound waves and movable back and forth with variations of pressure which are caused by water waves above the device, and an inertia microphone mounted within said chamber on said vibratory wall, and comprising a substantially closed casing containing granular material,

said casing having restricted vents in its wall, said vents causing equalization of pressure by permitting a iiow of air between the interior of said casing and said closed chamber as the vibratory wall is moved back and forth by the water waves.

In witness whereof, I have hereunto set my hand this 5th day of June, 1919.

ALBERT W. HULL. 

